Dry-running twin-shaft vacuum pump

ABSTRACT

Dry-running twin-shaft vacuum pump (1) with at least one pumping chamber (11, 12, 13), with a rotor pair (4-5, 6-7, 8-9) situated in the pumping chamber and borne by the shafts, and with a drive housing (21); in the pumping of toxic media, to limit the contaminated areas to components that are easy to assemble it is proposed that between the drive housing (21) and the adjoining pumping chamber (13) an intermediate plate be provided, which is traversed by the shafts (2, 3), contains the laterally exiting exhaust duct (52), and is releasable from the wall (17) of the drive housing (21).

BACKGROUND OF THE INVENTION

The invention relates to a dry-running twin-shaft vacuum pump with atleast one pumping chamber, with a pair of rotors situated in the pumpingchamber and borne by the shafts, with a drive housing which isassociated with one of the two ends of the pumping chamber, and withmountings which are situated in the section of wall of the drive housingfacing the pump chamber and support the two shafts which pass throughthis wall section.

"Dry-running" vacuum pumps are pumps whose pump chambers contain nolubricant or sealants. Their advantage lies in the fact that they canproduce vacuums completely free of hydrocarbons. However, it isimpossible to dispense with the lubrication of the bearings of theshafts which bear the pistons rotating in the pump chambers. Indry-running pumps, therefore, it is necessary to assure an effectiveseparation of the bearing chambers from the pump chambers. At the oneend of the pump the shafts reach all the way into the drive housing inwhich a drive synchronizing the rotor motion is situated. Also, thesealing off of the oil containing drive chamber from the adjacent pumpchamber must be assured.

On account of their particular property of being able to producehydrocarbon-free vacuums, dry-running twin-shaft vacuum pumps are oftenused in the semiconductor industry, namely in apparatus in which etchingor coating processes are performed under vacuum. The gases used orformed in these processes are often toxic. Maintenance or serviceoperations are therefore decidedly complicated by decontamination or thecontaminated parts of the pump.

EU-A-290,662 has disclosed a twin-shaft vacuum pump of the kindmentioned above. The drive housing adjoining the discharge-end pumpingchamber functions simultaneously as a bearing plate. Consequentlycontamination of parts of the drive housing is unavoidable. Beforeperforming installation work on the pump, therefore, these parts of thedrive housing must also be contaminated, which additionally complicatesmaintenance.

The present invention is addressed to the problem of creating atwin-shaft vacuum pump of the kind described above, in which a safeseparation between the drive chamber and the adjacent pumping chamberwill be assured and in which maintenance and installation operations canbe performed in a substantially simpler manner.

This problem is solved by the invention in that between the drivehousing and the adjacent pumping chamber an intermediate plate isprovided, through which the shafts pass, which contain a discharge linebrought out laterally, and which is removable from the wall of the drivehousing. In this system, additional means for separating the drivechamber from the adjacent pumping chamber can be provided between theshafts and the intermediate plate according to the invention. It ispreferable for the shafts to be equipped in this area with bushings,preferably piston-ring bushings. Another important advantage has to dowith the use of the pump according to the invention with toxic media.Due to the intermediate plate the contaminated part of the pump isclearly definable and separable from a noncontaminated area.

Pumps of the kind according to the invention, preferably with verticallydisposed shafts, are usually built up sectionally. Assembly begins withthe drive housing, the gears, shafts and drive bearings. This work callsfor great care and therefore it is tedious. Then the components androtors forming the pumping chambers are placed over the shaftssuccessively and then only have to be tightened. Through the use of theintermediate plate according to the invention the assurance is providedthat the complicated assembly part of the pump, namely the drivehousing, is not part of the contaminated area. The contaminated area islimited to the parts that are easy to remove and install. After theremoval of the contaminated parts the parts subject to wear (bearings,shaft sealing ring) are easy to reach. The drive housing, as thecomponent difficult to assemble, is protected both against contaminantsand against wear. Overall, a greater ease and simplicity of serviceprocedures are achieved by the invention.

Additional advantages and details of the invention are to be explainedwith the aid of embodiments represented in FIGS. 1 and 2.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a twin-shaft vacuum pump with an intermediate placeaccording to the invention, and

FIG. 2 an enlarged detail of a section of the shaft in the area of thedrive chamber and the adjacent pumping chamber.

The pump represented in FIG. 1 is a three-stage vacuum pump 1 with twoshafts 2 and 3 as well as three pairs of rotors 4 and 5, 6 and 7, and 8and 9. The axial length of the rotors decreases from the suction side tothe discharge side. The rotary pistons are of the claw type (Northey,cf. for example EU-A-290,662) and rotate in the pumping chambers 11, 12and 13 which are formed by plates 14 to 17 and the housing rings 18 to20. Plate 17 is formed by the wall section of the drive housing 21,which is associated with the discharge-end pumping chamber 13.

The shafts 2 and 3 are disposed vertically. This is also true of themotor 22 disposed next to the pump housing. Below the bottom bearingplate 17 the shafts 2 and 3 are equipped with gears 23 and 24 of equaldiameter which serve to synchronize the motion of the rotor pairs 4 and5, 6 and 7, and 8 and 9. The motor 22 also has a gear 25 on its bottomend. The driving connection is produced by an additional gear 26 whichis engaged with gears 24 and 25.

In the upper bearing plate 14 and in the wall 17 of the drive housing 21The shafts 2 and 3 are supported by rolling bearings 27. The top bearingplate 14 is equipped with a horizontally disposed coupling flange 28which forms the inlet 29 of the pump. The inlet passage 31 leads at itsend (opening 32) into the pump chamber 11 of the first stage. The outletopening at the end of the first stage is marked 33 and leads into theconnecting passage 34. The connecting passage 34 in plate 15communicates with the inlet opening 35 of the second stages. The bearingplate 16 is configured accordingly. Under the bottom (third) pump stageis the outlet 36 which communicates with the outlet opening 37.

Underneath the system consisting of pump housing and motor is the drivehousing 21 which comprises the oil-containing chamber 40 and the oil pan41. An oil pump 42 connected with the shaft 2 reaches into the drivehousing 21. Lubricant passages not shown in detail run from the oil pumpto those points in the pump (bearings, points of engagement of the gears23 to 26, retaining rings or the like) which require oil lubrication.The bearings 27 at the upper shaft ends are preferably greased.

The embodiment represented, of the three-stage twin-shaft vacuum pump,is water-cooled. To that end, cooling water passages 43 and 44 areprovided in the bearing plates 14 and in the drive housing 21 17. Thecooling water inlet and outlet are marked 45 and 46. The cooling waterinlet 45 is located at the lowermost point of the passage system 43, 44,so that easy drainage and complete emptying are assured.

The pump represented is equipped in the manner of the invention with anintermediate plate 51 which separates the drive housing 21 from theother components forming the pumping chambers 11 to 13. The intermediateplate 51 is removably fastened to the drive housing and itself forms awall section defining the pumping chamber 13. It contains the exhaustline 52 running laterally outward from the outlet opening 37. After theeasy disassembly of the components (including intermediate plate 51)forming the pumping chambers 11 to 13, which are contaminated if thepump is used with toxic media, all of the parts to be decontaminated aredisassembled. Decontamination of the drive housing, which is difficultto assemble, can therefore be avoided in service operations. Thebearings 27 and a radial shaft sealing ring 53 associated with each ofthe shafts, which is usually present, are located, as in the state ofthe art, in the wall section 17 of the drive housing 21. After theintermediate plate 51 is removed, these components are freely accessiblefor maintenance operations.

FIG. 2 shows an enlarged fragmentary section through a pump I accordingto the invention in the area where the shafts 2 and 3 (only one isvisible) pass through the bearing plate 16, the discharge end pumpchamber 13, the intermediate plate 51, and the wall section 17 of thedrive housing 21. To seal off from one another the adjacent chambers(pumping chambers and drive chamber), bushings 54 rotating with theshafts are provided, which have annular grooves 55 on their outer side.In the grooves 55 are the stationary piston rings 56 which together withthe grooves 55 form labyrinth seals.

The shafts 2, 3 are supported at a portion of greater diameter 57 on thebearings 27. This portion of greater diameter 57 is followed upwardly bya bushing 58 for the radial shaft sealing ring 53. This ring is heldexternally in an annular component 59 which is recessed into the wallsection 17 of the drive housing 21 and is fastened thereto. Between thebushing 58 and the piston ring bushing 54, i.e., above the radial shaftsealing ring 53, there is also a slinger disk 61 which protects theradial shaft sealing ring 53 against any falling dust particles.

At the level of the slinger disk 61, which is in the boundary areabetween the intermediate plate 51 and wall section 17, there enters asealing gas line 62 which passes through the intermediate plate 51,i.e., through an easy-to-cast component. Due to the feeding of sealinggas at this point, gas is constantly flowing through the labyrinth sealabove it toward the pumping chamber 13, so that toxic fluids beingpumped cannot flow in the opposite direction. In the state of the art itwas necessary to bring any necessary inert gas lines through the coolingpassages in the drive housing, in a manner which complicatedmanufacture.

In many applications of pumps of the kind here concerned it is desirablefor the walls around the pumping chambers to be as hot as possibleduring operation. There are limits to achieving this in the state of theart because the drive housing is cooled. However, as a result of theintermediate plate 51 according to the invention it is possible toseparate the drive housing thermally from the pumping chambers to a verygreat extent. This can be accomplished by making the intermediate plateof material that is a poor conductor of heat (e.g., gray cast iron,high-grade steel, or the like) and/or by taking measures ([by providing]gaps or the like) to reduce the contact area between the intermediateplate 51 and the adjoining components (ring 20, wall 17). In theembodiment according to FIG. 2, a plurality of grooves 63 are provided,one of which serves to accommodate a sealing ring 64.

We claim:
 1. Dry-running twin-shaft pump of a claw type comprising:atleast one pumping chamber having two ends; two shafts bearing at leastone rotor pair of a claw type situated in the at least one pumpingchamber; a drive housing associated with one of the two ends of thepumping chamber; a wall portion of said drive housing facing the pumpingchamber; bearings which are situated in the wall portion and support thetwo shafts which pass through the wall portion; between the drivehousing and the pumping chamber which is adjacent thereto, anintermediate plate removable from the wall portion and containing anaxial exhaust opening and a lateral exhaust duct communicating with theexhaust opening and through which intermediate plate the two shaftspass.
 2. Pump according to claim 1, in which the shafts are disposedvertically.
 3. Pump according to claim 1, which is multi-stage.
 4. Pumpaccording to claim 1, in which the shafts in the area of theintermediate plate have bushings.
 5. Pump according to claim 1, whichincludes associated with each of the shafts a radial shaft sealing ringwhich is situated between the bearings and the intermediate plate. 6.Pump according to claim 5, which includes a slinger disk disposed aboveeach of the radial shaft sealing rings.
 7. Pump according to claim 1, inwhich the intermediate plate contains a sealing gas line leading into aboundary area between the intermediate plate and the drive housing. 8.Pump according to claim 1, in which the intermediate plate comprisesmaterial that is a poor conductor of heat.